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Posts Tagged ‘layout’

In the ‘Custom Compiler Layout Assistants (Part 1)’ blog post, I profiled the use of the symbolic editor and how it makes placing devices that need to be in a specific interdigitated pattern (for example, a differential pair) very easy. With no constraints to enter and no code to write, layout is done in minutes vs. hours.

However, there is a lot more to the symbolic editor than the ability to simplify interdigitation. One good example is the ability to define multiple P and N row pairs and then symbolically chain and fold the transistors such that you get them to fit neatly in the rows. This is a key feature that allows you to not only control the aspect ratio of the design, but to very rapidly create a custom digital cell layout, as shown in Figure 1.

In the blog ‘Custom Compiler In-Design Assistants (Part 2)’, I outlined how we can use StarRC to report capacitances on critical nets in the layout even when the design is still in flux and not completely LVS-clean. In addition to capacitance reports, we also showed resistance reporting which is critical for FinFET-based layouts. At advanced nodes, the impact of parasitics, electromigration (EM) and restricted design rules drive critical layout choices. Interconnect that does not meet resistance, or EM criteria and unbalanced capacitances on matched nets, can and often does adversely impact layout schedules. So the earlier in the layout phase the layout engineer can address these issues, the sooner he or she can close the design.

EM in particular is a notorious problem in the FinFET process due to the high drive of the transistors and thin metals. So let’s say, for example, the layout engineer has to route a critical net which could be susceptible to the impact of EM. This is a non-trivial task that could be quite challenging. However, if you use Custom Compiler, there are some very cool capabilities that make laying out interconnect that meets EM criteria very quick and very easy.

As mentioned previously, on March 30th Silicon Valley was buzzing with excitement. Synopsys revealed Custom Compiler, a fresh approach to custom design that employs visually-assisted automation technologies to speed up common design tasks, reduce iterations and enable reuse at the SNUG Silicon Valley event. During this event, the R&D folks did a walkthrough of the technology ‘under-the-hood’ and showed the audience some cool layout assistants that leverage the graphical use model familiar to layout designers while eliminating the need to write complicated code and constraints. [Click here to view the videolog of the SNUG event.]

One of the layout assistants that was shown was the symbolic editor. This really is a must-have assistant when it comes to placing devices that need to be in a specific interdigitated pattern, like a differential pair. In the schematic, it is two symbols, but in the layout it could be hundreds of devices. The symbolic editor allows device placement to be edited in an easy and graphical manner and comes with a rich collection of predefined placement patterns. If you find a placement pattern you like, you can simply use it as-is and the symbolic editor will generate a correct-by-construction placement that you can instantiate in your layout. If you don’t find an exact match, you can easily use a pattern that is similar to what you need and rearrange the placement pattern graphically. No constraints to enter, no code to write and layout is done in minutes vs. hours.(more…)

I just wanted to take a moment to personally invite you to attend Synopsys’ Custom Compiler lunch event at DAC 2016 on Tuesday, June 7 in Austin, TX. At this event, engineers from GSI Technology, Samsung, STMicroelectronics, and Synopsys’ IP Group will showcase their experiences using the new Custom Compiler custom IC design tool with Visually-assisted Automation technologies.

As you’ll recall, Synopsys unveiled Custom Compiler on March 30 of this year at SNUG Silicon Valley. Custom Compiler is a new custom IC design solution that closes the FinFET productivity gap by cutting custom layout tasks from days to hours. It offers a fresh approach to custom design that employs Visually-assisted Automation technologies to speed up common design tasks, reduce iterations and enable reuse. Visually-assisted Automation technologies are a unique set of productivity aids that leverage the graphical use model familiar to layout designers while eliminating the need to write complicated code and constraints.(more…)

Over the last series of blogs we have looked at which tools the layout engineer has available to him/her to help deal with the complexity of doing layout with FinFETs. Even though there are tools that help, the fact is there is still a productivity hit when comparing the time it takes to do a FinFET-based layout vs. a planar CMOS layout. When I asked my layout colleagues “How much longer does it take to do a FinFET-based design vs. planar CMOS?”, they said it takes 2-3X longer.

So, if we are to recoup layout productivity when doing a FinFET-based design, which areas should we focus on? Well, let’s start at the very beginning, which, according to Julie Andrews in The Sound of Music, is a very good place to start. The task of generating the devices and placing them such that they meet all the design rules and will produce a robust working design is about 30% of the layout time. So if we can speed up this task then we will gain back some of the productivity we lost due to the complexity of the FinFET process.(more…)

Over the last few blogs I have outlined some of the productivity challenges that the FinFET process brings with respect to custom layout. Today Synopsys unveiled Custom Compiler and ushered in a new era of visually-assisted automation. Custom Compiler has all the good stuff I’ve been saying is needed in earlier posts: a new custom design solution that closes the FinFET productivity gap by shortening custom design tasks from days to hours.

This is not a revamp of the old constraint-based legacy approach, it’s a fresh approach to custom design that employs visually-assisted automation technologies to speed up common design tasks, reduce iterations and enable reuse.

Continuing on the theme of FinFET layout, let’s consider what you have to do for routing. Again drawing on the experience of my layout colleagues who are still ‘in the business’ and dealing with FinFETs, here are a few landmines you will have to deal with.

One particular issue they encounter is that although the base layers have shrunk considerably, the shrink of the routing layers has not kept pace. Each new node has brought us smaller transistors, but the minimum metal pitch has not really changed. This really impacts layout floorplanning because designs that were once dictated by device area are now dictated by the ability to route the required signals. Double-/triple-patterning compounds the issue even further.(more…)

So, FinFETs rule! They give the designer so much flexibility in trading off power and performance that it should be a no-brainer to adopt the technology–right?

Well, every silver lining has to have a cloud, and in the case of FinFETs there are quite a few.

I polled a number of layout designers who have first-hand experience of laying out FinFET designs and asked them “What’s the impact of FinFET?”. Here’s what they told me requires them to do extra work:

First off is the sheer number of rules that they have to be conscious of. The number of rules has more than doubled compared to a 40-nm process. Of special concern are some of the density rules that now have to be applied to a lot more layers.

Another area you have to pay particular attention to is maximum diffusion space. This forces devices to have guardrings around them so that you do not have too large a diffusion space. The diffusion in the guardring essentially breaks the space check. So you either have to have devices very close together or spaced by guardrings.

Process restrictions require that every fin has to have an equal height. In addition there are strict limitations on the sizes of “W” and “L” that can be used. As a result a device that requires a large “W” (width) has to be quantized into multiple fin units that utilize the acceptable “W” and “L”.
What this means in practice is that an innocent-looking single device in the schematic can be 100 devices in the physical layout! Add to that the fact that fins have to snap to specific grids and you have a massive layout challenge for even a simple circuit.

In my last post, I said: “A hurricane has made landfall and its name is FinFET”. OK, it’s a little corny, but it was not meant to convey a sense of impending doom for custom layout productivity. No question that hurricanes are disruptive, but humans can adapt to even the worst nature can bring. And FinFETs bring tremendous benefits along with the disruption.FinFETs are without doubt the most radical shift in semiconductor technology in decades, but moving to FinFETs is absolutely necessary. As feature sizes became finer, high leakage current due to short-channel effects threatened to put the brakes on scaling. FinFETs address the leakage issue and give Moore’s Law a new lease of life.Today the bulk of design starts are at the established nodes above 28 nm, so not everyone doing custom layout has experience with FinFETs. For those who have not yet felt the ‘winds of change’ that FinFETs bring, here is a brief primer.

I left off in part 2 of this blog asking the question: “Have we exhausted all avenues in our search for layout productivity?”

Although there has been no revolutionary technology as with the initial CALMA systems, there have been some incremental improvements that help oil the gears when doing layout.

On-line DRC has been one such improvement. Having the ability to check the layout for design rule violations incrementally, as you complete more and more of the design, made it easier to implement changes. Violations were displayed in the layout, making it easy to find and fix them. However, checking the layout connectivity versus the schematic was still a batch task that could only be run when the design was fully implemented. The connectivity of the physical layout had to be extracted in order to compare against the logical connectivity.

As EDA marched on, with each new crop of more powerful workstations came the next generation of interactive tools. If you could compute the design rule checks fast enough, why not show them dynamically as layout geometries were being created? And so Design-Rule-Driven (DRD) layout was born.(more…)